1. Field of the Invention
The invention relates to the construction of electric furnaces and, more particularly, to an electrode-slipping apparatus for use in such furnaces. The invention is readily adaptable for application in ferrous and nonferrous electrometallurgy, as well as in the chemical industry where use is made of electric furnaces furnished with self-baking or pressed electrodes.
Electric ore-smelting furnaces are equipped with pressed (carbon or graphite) or Soderberg self-baking electrodes. The electrodes in question function as current conductors and the carbonizable material thereof is used as a reducing agent in chemical reactions proceeding in the furnace hearth.
To make up for the burning of electrodes in the furnace hearth, the furnace is provided with electrode-slipping mechanisms.
As a rule, these mechanisms permit an electrode to be slipped by a single step for a length of 80 to 100 mm, the electrode-slipping operation being performed 3-4 times a day.
It has been found by test and trial that the electrode-slipping practice described above is disadvantageous in that it results in the breaking of electric contact between the electrode and the contact shoes. This in turn brings about vigorous liberation of a great amount of heat and leads to substantial losses of electrical energy, whereas rapid displacement of the electrode tip in the furnace hearth upsets normal power conditions as well as process conditions as a whole.
It takes considerable time (one hour and more, depending on the stroke and rate of the electrode slip) to reestablish normal electrical contact and technological process.
With the use of Sonderberg self-baking electrodes, the temperature within the electrode tends to change sharply, thereby affecting the disposition of the coking zone and quality of the electrode coking mass. It often happens in practice that in the course of slipping of the insufficiently baked electrode, the electrode, when extended beyond the boundary of the lower edge of contact shoes, is broken.
As a result, the furnace is rendered inoperative for a long period of time and the yield of the end product is materially diminished. In view of an ever increasing power capacity and production output of electric furnaces, the aforesaid dificiency is utterly condemnable.
It has been found advantageous, as the electrode is consumed in use, to carry out the electrode-slipping procedure in a manner permitting continual slipping of the electrode at a rate equal to that of its consumption.
2. Description of the Prior Art
For example, there is known an electrode-slipping apparatus for use in electric furnaces (cf. U.S.S.R. Inventor's Certificate No. 182,749). This apparatus comprises steel bands welded to a metal casing of self-baking electrode, and gripping means. The apparatus of this type has been found suitable for use in electric furnaces with a power capacity ranging from 6.5-7.5 to 12.5 mvA. Here, the electrode is slipped intermittently at half-an-hour intervals for a length of 12 mm, or at intervals of 45 min for a length of 16 mm. This electrode-slipping method proved inefficient due to the outdated construction of the device for effecting same, and is also unsuitable for use in electric furnaces of higher power capacity.
There is also known an electrode-slipping apparatus (cf. catalog "ING Leone Tagliaferri", Italy), which comprises a slide valve set in the hydraulic fluid pressure and drain line of the electrode-slipping hydraulic mechanisms, a slide valve and pressure-reducing valves set in the hydraulic fluid pressure and drain lines of a hydraulic mechanism for actuating contact shoes, and a programming unit.
With this apparatus it becomes possible to effect the electrode-slipping operation intermittently at a rate of 30 to 40 mm per hour at carbide furnaces operating under steady-state conditions and wherein the automatic power regulator means is cut off with the aid of the same hydraulic cylinders used for automatic power control, effected through displacement of the electrode. At the moment of slip, the electrode retains its original position while the contact shoes are slidably moved upwardly along the electrode.
The apparatus described above is disadvantageous in that it fails to provide for automatic electrode slipping operation under loading conditions, and does not ensure steady-state operating conditions of an electric furnace.
In addition, the aforedescribed devices fail to ensure production of high-quality electrodes.
Furthermore, there is no future for devices which comprise bands, since their application is associated with larger operating heights of shopworks required to enable installation of electric hoists on a special floor above the electrode-slipping mechanism. An increase in the height of a workshop by 4 to 6 m is economically unprofitable.
The Wisdom band-utilizing device operates under the action of the electrode weight. The bands required to support the electrode are unwound from a reel actuated by a drive means, and are then pulled through a system of grip blocks solely under the action of the electrode gravity. If, however, the electrode is stuck in the area of a contact assembly, this being quite a frequent occurrence with spring-biased power-driven contact shoes, then, in this case, the tension of the bands will decrease to result in the collapse of the electrode, which, in turn, may result in the breaking of the bands; in other words, a constant control over the device operation and a safe blocking system are required, which makes the apparatus as a whole complicated in operation.
To avoid the electrode jamming, it has become an adopted practice to release springs acting to press the contact shoes against the electrode surface.
However, the contact between the contact shoes and the electrode is impaired, power losses are increased at a point of contact and the life service of the contact shoes is markedly decreased. In the case of electric furnaces with a power capacity of 16.5 mvA and over, wherein the current in the electrode is as high as 60,000 A and above, the loosening of contact between the contact shoes and the electrode during steady-state operation of the furnace is absolutely impossible.
The electrode-slipping device employing steel bands is in constant demand for additional use of manual labour and higher consumption of metal. Even with faultless operation of its mechanisms and programming unit, a constant control and periodic welding of the steel band to the electrode casing is required as the electrode is consumed in use. This in turn leads to an excessive consumption of metal required for the bands and welding electrodes. There are known technological processes (for example, production of aluminosilicate) where even a small amount of iron in the furnace bath is highly undesirable, since it impairs the quality of the and product.
The steel bands welded intermittently to the surface of the electrode casing get between the contact shoes, thereby impairing their contact with the electrode and thus increasing the rate of wear of the contact surface of the contact shoes.
Therefore, the prior-art device for carrying out the method of continual slipping of electrode through the use of bands is but a partial solution to the existing problem and lacks universality. To be more exact, the device in question is suitable solely for slipping self-baking electrode by means of bands in accordance with the Wisdom system. A pressed electrode, for example, is impossible to suspend and slip by means of bands.
The band operating device makes it possible to effect only downward slipping of electrode, preventing return or upward movement thereof, for instance, in a case of its breaking.
In the above-described device no provision is made to ensure the independence between the rate of the electrode slipping and the rate of its consumption.